I'm afraid I don't have specific experience with that. I imagine that larger scars would be similar and I think that burn scars leave an area of skin that is a different tone and shinier, but in both cases, I would definitely recommend looking for reference. Art is above all teaching yourself to see.

I am afraid I will not be of much help with that. The key will be to look at plenty of reference and then find a way to recreate that. Sorry, I know that is vague, but that is all that I did here, looking both at photo reference and especially in person to see how light interacts with the different skin.